Shielding device for ignition or similar circuits



June 8,1937. "r. B. HOLLIDAY 2,032,300

SHIELDING DEVICE FOR IGNITION OR SIMILAR CIRCUITS Filed June 29, 1933 INVENTOR 779:0 DORE 5.Ho1.z./a,4v

Patented June 8, 19 37 UNITED STATES PATENT OFFICE. I

SHIELDING DEVICE FOR IGNITION OR SIMILAR CIRCUITS Theodore B. Holliday, Dayton, Ohio Application June 29,1933, Serial No. 678,249

14 Claims. (01. 123-148) (Granted under the act or March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) I mission systems such as disclosed in the patent to Crook No. 1,645,643, in which a generator of electricity and a receiving instrument are disposed within a' closed chamber and electrically connected in such a manner as to effect a nongrounded electric transmission line. In this system, the negative transmission line serves as a shielding to prevent the emanation of electromagnetic field and its consequent disturbance or interference with other and separate receiving instruments 'by utilizing the opposing efiects of currents in opposite directions, but the system does not provide for the elimination of the electrostatic disturbance of the negative line or the combined electrostatic disturbance of both positive and negative transmission lines. It is also well known that grounded electric transmission lines of highvoltage have been provided with metallic shielding to reduce physical hazard and only partially the electrostatic and electromage netic disturbances by grounding the shielding,

-' The invention is shown by way of example-in tion to provide in combination with a grounded,

electric transmssion line of high voltages a 'metallic shielding that will practically entirely eliminate electromagnetic disturbances, prevent electrostatic disturbances, and safeguard again-st the breakage, abrasion and corrosion of the negative conductor of thetransmission line, which otherwise would be dangerous to life and limb of individuals in contact therewith.

the accompanying drawing in connection with a magneto, as the generator of a high voltage, and a spark plug as the receiver, it being understood that the invention is applicable'to any high voltage transmission system.

In the drawing:

Fig. 1 is a diagrammatic perspective view with parts broken away and in section, showing my invention as applied to an airplane magnetic circult.

Referring more particularly to the drawing the numeral l designates a closed shielding that consists of a grounded metal. chamber 2 completely enclosing a source of high voltage such as a magneto' 3, and a conduit 4, one end of which opens out into the chamber 2 and being electrically connected therewith. The other end of said conduit is adapted to receive a receiving instrument, such as a spark plug and is grounded to the engine (not shown) through intimate engagement with the base of the spark plug 5.

A shielded cable 6 for efiecting'an electric cir- 1 cuit between thesource of high voltage and the receiving instrument is disposed within the con' duit 4 and is insulated therefrom at and between points 1 and IS, the wire 9 of the cable constituting-the supply or positive lead and the metal braided shielding l0 constituting the return or negative lead. The conduit is preferably con.-

' structed to be flexible and for this purpose it may be made of braided metal.

As illustrated herein the source of high voltage comprises a primary winding (not shown) and, a secondary winding 8 inductively. electrically coupled with the primary winding but not grounded therewith; The positive and negative leads of the secondary winding are respectively electrically connected to the wire lead 9 and metal braided shielding H) of the cable 6, the lead in turn being connected to the central electrode terminal l l of the spark plug and the shielding being grounded to the spark plug through. a shielding neck portion," to receive the cable 6 and to pro -vide intimate electrical engagement with the cable shielding Ill. The cap is insulated from the central electrode of the spark plug. By this arrangement the current runs from the secondary winding 8 over the wire 9 to the gap between the electrodes of the spark plug whence the high voltage created at the magneto causes the current to jump the gap and flow back to the secondary windingthrough the spark plug cap l3, the extension cap l2, the shielding Ill and the lead IS.

The outer shield issuitably insulated from the inner shield by means of a dielectric, such as air, rubber, porcelain, or-the-like, at all points except at points I! and I3 at the base of the spark plug where both inner shielding l0 and outer shield ing 4 are connected together and to the spark the chamber 2 and conduit 4, is grounded at:a number of closely spaced points along their ef-.- fective length.

, Having" thus described my invention, what-I 9 claim is:

1. Incombination with an electric circuit having a supply line andra return line electrically insulated therefrom and a receiving instrument electrically connected in said circuit between said lines, the said return linebeing grounded only at'one end and both of said lines being so arranged that the magnetic field of theone is neutralized by that of the other, of a shielding enclosing said lines, said shielding being both electrically insulated from the supply line and grounded substantially throughout the entire length of the enclosure.

2. In combination with an electric circuit having a supply line and a return line electrically insulated therefrom and a receiving instrument electrically connected in said circuit between said lines, said lines being so arranged that the magnetic field of the one is neutralized by that of the other/of a metallic shieldingenclosing said lines and electrically insulated therefrom at all points except for an electrical connection between the return line and theshielding'at one end of the latter substantially at the connection of the return line with the receiving instrument, said shielding being grounded at its point of electrical connection with the return line and at closely spaced points substantially throughout the entire length of the enclosure;

3. In an electric circuit system, the combination with a source of current supply of a receiving means remote therefrom, a connecting circuit to transfer energy from said source to said receiving means and including a supply line and a return line insulated from each other, said connecting circuit having the return line grounded only at one end thereof and concentrically enclosing the supply line for a portion of the length thereof whereby the magnetic field of the one is neutralized by that of the. other throughout said length, and a ,shield grounded substantially throughout its length and enclosing said lines to prevent elec-' trostatic disturbances thereof.

v receiving means and including a supplyiline and; a return line insulated from each' other, said 4. In an electric circuit system,- the combination with a source of current supply of a'receiving means remote therefrom, a closed connecting circuit to-transfer energy from said source to said receiving means and including a Supply line and a return line insulated from each other, said connecting circuit having the return line grounded only at one end thereof and concentrically enclosing the supply line. for a portion of the length thereof whereby the magnetic field of the one is neutralized by that of the other through out said length, and a shield grounded substan tially throughout its length and substantially insulated from but enclosing said lines and said source'of. supply turbances thereof.

In an electric circuit system, the combination with a source of current supply of a receiving means remote therefrom, a connecting circuit to transfer energy from said a source to, said connecting circuit having the return line thereof concentrically enclosing the supply line throughout the length thereof whereby the return line serves as a shield for the supply line throughout said length, and "a, metallic covering enclosing said lines and said sourcfof supply to providean parts at all other'points.

to prevent electrostatic 'disouter shield therefor to prevent electrostatic disturbances thereof, said last-mentioned shield being insulated from the said source and the said lines at all points except "for a joint connection with the return line and with the ground at one end only, said covering being additionally and f separately grounded at closely spaced points.

6. In an electric circuit system, the combina tion with a source of current supply of ,a receiv-- ing means remote therefrom, a closed connecting enclosing the supply line for a portion of the length thereof whereby the-magnetic field of the one is neutralized by that of the other throughou' 1 said length, and a shield grounded substantially throughout its length and enclosing said lines o and said source of supply andsaid receiving means to prevent electrostatic disturbances thereof said grounded shield being in electrical contact with the grounded end of the return line at one end and being insulated from the enclosed '7. In an ignition system, a high tension source neither terminal of which is grounded, a spark plug, a shield mounted upon and grounded through said spark plug, a high-tension lead from one terminal of the said source to the spark plug provided with a shielding cover of metal braid connected to the other terminal of the high tension' source at one end and to the spark plug shield at the other end, and a grounded shielding enclosing the high tension source and the shielded hightension lead and the spark plug shield and having a ground connection with the spark plug and spark plug shield substantially at the base of the shield, said grounded shielding being insulated from the high-tension source and the shielded high-tension lead and the spark plugshield at all points except at the ground connection with the spark plug and spark plug shield.

8. In an ignition system, a grounded metal chamber, a, generator enclosed in said chamber and including a. high tension source neither ter-' minal of which is grounded, a grounded spark plug, a shielding cap on said sparkplug having electrical contact with the grounded portion of the spark plug but insulated from the central electrode of the said plug, connecting one terminal of the high tension source with the central electrode of the spark plug and having a double'cover of metal braid shielding, withthe inner shielding connected to the bther terminal of thehigh tension source atone end and to the spark plug shielding cap at the other end and the outer shielding connected to the grounded container at one end and to the spark plug and spark plugshielding cap at the other end and substantiallyit the point where the said cap'has groundconnection with said plug; said inner and outer shielding being in-- sulated from each other and from the high-tension wire at all points except at the ground connectionwith the spark plug.

a high-tension wire 9. In a shielded ignitio'n system, a grounded metal chamber, a grounded spark plug, a gener.-

ator e'nclosedin said chambe and including a overin'g providing inner and outer shields, the inner shield being neto casing, a grounded spark plug'and a high tension cable consisting of a high-tension wire A said inner and outer shields being insulated from each other and from the high-tension lead at all points except at the ground connection with the I ranged .to neutralize the magnetic field of one by spark plug.

10. In a shielded ignition system, an encased high-tension magneto having the secondary' high-tension source ungrounded within the magconnecting one terminal of the secondary'hightension source with the central electrode of the spark plug and enclosed in a metal braid shielding connected to the other terminal'ot the secondary high tension source at one end and to a grounded portion of the said spark plug at the other end to provide a return path for the ignition current.

ll. Inncombination with an electric circuit having a supply line and a return line electrically insulated therefrom and a receiving instrument electrically connected between said lines, the return line being grounded only at one end and being so disposed with respect to the supply line that the magnetic field of the one isneutralized by that of the other, of shielding meansenclosing said circuit and being both electrically insulated therefrom and grounded substantially throughout its length to prevent electrostatic disturbances thereof. g 12. In combination with an electric circuit having, a supply line {and a return line, the one line being enclosed by the other and electrically insulated therefrom and the said other line being grounded only at one end, of shielding means enclosing said lines and being both electrically insulated therefrom and grounded substantially throughout their entire length to prevent electrostatic disturbances, thereof.

13. An electric ignition system having a hightension source neither terminal of which is grounded, a spark plug, supply and return leads connecting corresponding terminals of the hightension source and spark plug,-said leads being electrically insulated from one anotherand arthe other, and a metallic shield substantially en-v closing said leads and spark plug and electrically connected. with the spark plug directly around the point where the return lead connects to the spark plug but being both electrically insulated from said leads at all points except at the connection to the spark 'plug and grounded at said connection and throughout the length thereof.

14. An electric ignition system comprising a grounded shielding chamber, a non-grounded source of electrical energy within and insulated from said grounded shielding chamber, a grounded spark plug, supply and return leads connectconnected with the return-lead and with thesaid spark plug at the other end, said shield being both electrically insulated from said leads at all points except at the said connection with the return lead and spark plug and grounded throughout the length thereof.

THEODORE "B. HOLLIDAY. 

